Infrared based systems have found widespread appeal in wireless communication systems including mobile point-to-point and LAN (Local Area Network) applications. Communication interconnections in a wireless communication system utilizing infrared are set up using infrared (IR)transceivers. A station, e.g. a personal computer (PC), notebook computer or mobile communication device, is connected/coupled to a transceiver. The infrared transceiver includes at least one infrared light emitting diode (LED), and typically comprises one or more photodiodes responsive to the output wavelength spectrum of the LED in the transceiver of the other party's communication station or device.
The performance and integrity of an infrared communication link will depend on the communication distance and communication protocol being utilized in addition to the operating environment, particularly the ambient light.
Known infrared communication transceivers comprise an infrared configuration controller and are typically implemented as one or more integrated circuits, i.e. chips. The configuration controller configures the system parameters such as bandwidth, sensitivity and drive current. In existing systems, external fixed components such as pull-up and pull-down resistors are utilized in conjunction with the configuration controller to set the system parameters, i.e. sensitivity, bandwidth, and drive current for the infrared light source (i.e. LED).
The known infrared communication chips suffer a number of drawbacks. First, it is difficult to optimize the infrared chip for operation on different communication protocols because one set of fixed external components sets the system parameters. Operation at a different communication protocol requires a new set of external components. For example, the well-known Apple Talk network communication protocol utilizes a conventional irDA chip and an external pull-down resistor of 2.7 kohm to set the optimal bandwidth. For other known IR communication protocols, a 130 kohm pull-down resistor is needed for optimum performance. One solution to this problem involves using one or more external analog switches for connecting/disconnecting the resistors. The drawback with this approach is the increase in footprint and larger PCB size required. Any increase in size is impractical for most applications, particularly a PCMCIA card.
Another problem with existing systems is the inability to change the system parameters "on-line", i.e. without changing the hard-wired or `jumpered` resistors. However, in practical applications the infrared communication system is called on to handle various operational environments. For example for an infrared mobile telephone the communication distance may vary from 1 cm to more than 1 meter, and the input signal amplitude range can span 5 orders. The problem which arises is the difficulty of finding a set of system parameters which meet the requirements for the various operational environments. In known systems, the LED driving current is typically set to the value which meets the requirement of the maximum communication distance. If the infrared communication interface is not operated at the maximum communication distance, then a wastage of electrical power results. In addition, the receiver becomes saturated when the actual communication distance is less than the maximum. For example, known infrared transceivers in an Apple Talk-based network can achieve a maximum distance of more than 1.5 meters, but at a distance of around 20 cm, a fading zone of 4 cm exists due to the very strong input optical signal. To eliminate the fading zone, the sensitivity control resistor must be changed from 162 kohm to 1.8 kohm. However, the maximum communication distance is also reduced from 1.5 meters to 0.56 meters. Thus, adapting the transceiver to short communication distances to eliminate the fading zone also eliminates the ability to operate at larger distances.
Another problem with existing infrared communication chips is the inherent unsuitability to automatic chip testing. Often it is desired to test the chips based on customer requests or quality requirements in order to find the optimal setting for some special communication conditions. To determine the optimal operational requirements, a set of external resistors are soldered to the PCB and connected to the infrared communication chip. The chip is then tested, and if not acceptable, the resistors are removed and a new set are installed and the test is repeated. It will be appreciated that this is a tedious and time-consuming exercise better suited to an automated system.
The present invention addresses these disadvantages and shortcomings with the prior art.